The ill effects of glue residue can range from yellow toning to environmental damage.

Residues are not only unattractive but, more importantly, can create permanent surface changes that will damage the coins we value. While many residues do not have specific causes some do. Glueresidue can actively change the surface chemistry of a coin and, if not removed, leave it ineligible for NGC grading.

Glue residue is often a raised substance on the surface of a coin and usually on one side in a specific location. The substance is typically a different texture than the coin's original metalsurface. With time, glue residue will yellow leaving an unappealing visual indication. Many times, though not always, glue residue will be sticky to the touch and attract further dirt and lint fromthe immediate environment.

A coin can acquire glue residue from a myriad of scenarios. These may include mounting in a holder or frame with a hardened liquid adhesive or held in place with a strip of transparent tape. Coinsmay have been secured by various adhesive substances for display or storage when it was used in daily commerce and long before it had any additional numismatic value.

When glue residue is present, professional removal is recommended. Removing glue residue can come with some concerns. Most of the time glue residue can be removed from the surface leaving a clean,relatively damage free surface. Many times, however, the glue substance can affect the surface. The result may range from a pattern in the toning to irreversible environmental damage in a clear shapewhere the glue was. When the visual difference is a case of toning, steps can usually be taken by the NCS conservators to minimize the impact. Permanent environmental damage, however, cannot beeasily minimized.

Glue residue can sometimes be mistaken for a mint error. This is especially true if the glue residue has the impression of another coin in it appearing as a sought after multiple strike minterror. The glue containing the secondary image will be yellowed and will be at least somewhat transparent to see the true surface of the coin. This thick type of glue will often contain air bubblesthat even when tiny are observable. The secondary image will also have the visual texture difference even if it's a shiner matte appearance compared to the tie surface of the coin. Glue removalwill be recommended in cases where it is masquerading as a mint error.

To read the complete article, see:
NCS Conservation: Glue Residue (www.ngccoin.com/news/article/5833/NCS-conservation-glue-residue/)

To read the earlier E-Sylum article, see:
NGC NUMISMATIC CONSERVATION SERVICES (www.coinbooks.org/esylum_v19n52a16.html)